Rotax PTO Taper?

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Armilite

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Rotax used mainly 30mm 1:10 PTO Taper for most of its 2 Strokes. The 670 and Newer Engines use a 33mm 1:7.5 PTO Taper. Now I have had a lathe for 25+ years and never did a Taper. I have a Steel Pulley that has a Straight Hole and I want to fit on my 277 PTO, but I don't have a 277 PTO Drawing. I'm wondering if I can just buy a 30mm 1:10 Reamer and Drill Bit to do this.

I found this Taper Calc. Under 10% they show 1:10 = 5° 43'. On the drawing, they show Big End as 29mm/1.141729" OD, and Flute Lenght 19.5mm/0.7677142" which Calc shows end as 27.05mm/1.064957"
http://www.magafor.com/841/uk.htm

So am I Thinking right? Do I look for a 30mm 1:10 Taper Reamer or a 29mm 1:10 Taper Reamer? The Steel Pulley Hole Mic's out at 22.16mm so to Ream it, I probably should drill it closer to just under 27mm. I want to practice on some Scrap Aluminum Stock first. The Pulley has a depression on the front and an extension on the Back, front to back is about 35mm.

Here is a 503 PTO Spec's.
Rotax 503 PTO.jpg Rotax Taper 30mm 1_10.jpg Tapers.jpg

Bought 8 Groove Diesel Truck Alternator Serpentine Belt Pulley 2.37O.D .875  ID - 3.jpg
 

n3puppy

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Jun 25, 2019
Messages
130
1:10 taper is 1:10 taper regardless of starting point

277 is 30mm because that is the crankshaft thickness at the straight point (6206 bearing 30mm ID)

You can use a 29mm reamer - the pulley just won't slide on as far before being fully mated to the crankshaft

Seems to me you need to decide how far out the engine side of the pulley needs to be for belt clearance with other engine parts to figure where you need to drill/ream etc

Snowmobile clutches spec pulley offsets even though they are all 30mm 1:10 tapers.
29mm reamer would look like the first two examples of clutches
30mm reamer would look like the "Flush" clutch
Drill a big hole first then 30mm reamer if you want pulley closer to engine. (Last two examples)87165B8F-D15F-4363-9085-41CEC97FE5E2.jpeg
 

Armilite

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Joined
Sep 5, 2011
Messages
3,267
Location
AMES, IA USA
1:10 taper is 1:10 taper regardless of starting point

277 is 30mm because that is the crankshaft thickness at the straight point (6206 bearing 30mm ID)

You can use a 29mm reamer - the pulley just won't slide on as far before being fully mated to the crankshaft

Seems to me you need to decide how far out the engine side of the pulley needs to be for belt clearance with other engine parts to figure where you need to drill/ream etc

Snowmobile clutches spec pulley offsets even though they are all 30mm 1:10 tapers.
29mm reamer would look like the first two examples of clutches
30mm reamer would look like the "Flush" clutch
Drill a big hole first then 30mm reamer if you want pulley closer to engine. (Last two examples)View attachment 92725
=============================================

Yes, I have been looking at that distance using a 503 CAD Drawing. The PTO Shaft for the Bearing is 30mm, but the Big End start of the Taper is 29mm. On the 503 I can easily have a, .818" / 20.99mm Thick Back Plate with plenty of spacing. ACE Belt Drive I think is 19mm

Another Option is, to Bore Pulley Hole Bigger and to use the Clutch Steel Shaft that has the proper Taper and just turn OD down if needed and Press on the Pulley, then Weld it. I have one of those Shaft for a 670, but not for the 277. That way I could move the Pulley Outward to use a Thicker Back Plate. For a 277 (25-35hp), I would like to have a minimum 3/4" / 19.05mm Backplate.

Rotax 503 Pulley Side View - 1.jpg Belt Drive Pulley on PTO.jpg
Belt Drive Pulley move up 2.jpg Belt Drive Pulley move up 1.jpg
 

Armilite

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Joined
Sep 5, 2011
Messages
3,267
Location
AMES, IA USA
Wall thk. of original......will there plenty wall thickness of the modified pulley.
From the picture it doesn't look like a problem.
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Yes, plenty of material and it's Steel not Aluminum that most use. Off a Diesel Truck Alternator. My Plan is to make this for the 277 depending on what's done to it, but Max 6500rpm, and making it for Stock 25.4hp@6000rpm to 38hp@6500rpm. If you did the Bigger 38mm Carb, rpm Increase to 6500rpm, some Cylinder & Case Mild Porting, with a Good Tuned Pipe you can see 38hp. If you Big Bored it to Max 82mm you can see a lot more hp. Stock 277 with 11.8cr is 268.8cc/7cc = 38.4hp and Big Bored to 82mm = 348.6cc/7cc = 49.9hp. Big Bored to 82mm and Stroked to 70mm = 369.8cc/7cc = 52.8hp.

Simonini Victor 1 Singles, 362cc with 9.5cr = 44hp, 382cc with 9.5cr = 48hp, 400cc with 9.5cr = 54hp!
 
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